This invention relates to composite powdered materials having a metal (or alloy) matrix phase and one or more reinforcement phases. At least one of the reinforcement phases is formed insitu as a reaction product. This invention relates also to a process for producing the composite powdered material in which one or more of the reinforcement phases are formed insitu as powders containing the reactant constituents are passed through a high temperature zone. More particularly the high temperature zone is a plasma jet.
Metal matrix composites consist of intermetallic or ceramic phases dispersed in a metal or alloy matrix in which the combination results in improved or unique properties which could not be achieved using the individual components alone. The choices of the individual phases and their respective amounts depends on the desired physical, chemical, and/or mechanical properties of the product. For example, discontinuously reinforced metal matrix composites are attractive for applications requiring high strength levels at elevated temperatures. The reinforcement phase is selected for its high strength and high hardness and is typically an oxide, carbide, and/or a nitride. Typically these phases have very high melting points and are thermally stable in the alloy matrix. They are incorporated into the composite system by mechanical mixing with the alloy powders. Silicon carbide whisker or particulatereinforced aluminum alloys are fabricated using the composite approach. The process for fabricating whisker reinforced materials on a commercial basis has been developed by ARCO Metal's Silag Operation. A process for making particulatereinforced aluminum alloys has been developed by DWA Composites Incorporated. It utilizes a binder to make green "pancakes" of SiC and aluminum powders which are then stacked prior to hot pressing. U.S. Pat. No. 4,259,112, Dolowy, J. F., Webb, B. A., and Suban, E. C., Mar. 31, 1981.
Though specific details may differ, the powder metallurgy approach to making composites is based on mechanical mixing of the metal matrix and the reinforcement phase powders and subsequent consolidation.
Another composite technique called "compocasting" involves adding non-metals to partially solidified alloys. The high viscosity of the metal slurry prevents particulates from settling, floating, or agglomerating. Bonding of non-metal to metal is accomplished by interaction between the respective particles. Mehrabian, R., Riek, R. G., and Flemings, M. C., "Preparation and Casting of Metal-Particulate Non-Metal Composites", Metall. Trans., 5(1974) 1899-1905, and Mehrabian, R., Sato, A., and Flemings, M. C., "Cast Composites of Aluminum Alloys", Light Metals, 2 (1975) 177-193.
Still another method for producing powder metallurgy composite materials is by mechanical alloying. This is essentially a high energy ball milling operation which is done typically in a stirred ball mill called an attritor mill. High strength material results from mechanically working the alloy, because of incorporation of oxides and carbides during the milling, and strengthening mechanisms due to severe working resulting in fine grain and sub fine grain size.
U.S. Pat. Nos. 3,909,241 and 3,974,245 relate to processes for producing free flowing powders by agglomerating finely divided material, classifying the agglomerates to obtain a desired size range, entraining the agglomerates in a carrier gas, feeding the agglomerates through a high temperature plasma reactor to cause at least partial melting of the particulates, and collecting the particles in a cooling chamber containing a protective gaseous atmosphere, wherein particles are solidified.